The present invention pertains to a copper alloy sputtering target for a wiring material of a semiconductor element, in particular a copper alloy sputtering target which allows the formation of a seed layer being stable, uniform and free from the occurrence of coagulation during copper electroplating and which exhibits excellent sputtering film formation characteristics, and a semiconductor element wiring formed with such a target.
Conventionally, Al (specific resistance of roughly 3.1 μΩ·cm) has been used as the wiring material of a semiconductor element, but copper wiring with lower resistance (specific resistance of roughly 1.7 μΩ·cm) has been put into practical application pursuant to the miniaturization of wiring.
With the current formation process of copper wiring, often times, after forming a diffusion barrier layer of Ta/TaN or the like in a contact hole or the concave portion of a wiring groove, copper is electroplated thereto. In order to perform this electroplating, as the foundation layer (seed layer), generally, copper or copper alloy is sputtered and deposited thereto.
Ordinarily, electrolytic copper having a purity of 4N (excluding gas components) is employed as the crude metal in a wet or dry high purification process to manufacture high purity copper having a purity of 5N to 6N, and this was used as the sputtering target. Here, there was no particular problem for copper wirings having a semiconductor wiring width of up to 0.18 μm.
Nevertheless, there were problems in that with ultra fine wiring where the copper wiring width is 0.13 μm or less; for instance, 90 nm or 65 nm, and the aspect ratio exceeds 8, the thickness of the seed layer would become an ultra thin film of 100 nm or less, and, when forming a seed layer with a 6N purity copper target, coagulation would occur and a favorable seed layer could not be formed.
As described above, the uniformity of the foundation layer is important, and, when the foundation layer becomes coagulated, it is not possible to form a uniform film upon forming a copper film via electroplating. For example, during wiring, defects such as voids, hillocks, and disconnections are formed.
Even if defects such as voids described above are not formed, since an uneven electrodeposited texture of copper will be formed in this portion, there is a problem in that the electromigration resistance will deteriorate.
In order to overcome this problem, it is important to form a stable and uniform seed layer upon performing copper electroplating, and a sputtering target optimal in forming a seed layer having superior sputter deposition characteristics is required.
Heretofore, as the copper wiring material, a method has been proposed of adding certain elements to copper in order to improve the electromigration (EM) resistance, corrosion resistance, bond strength and so on (for example, c.f. Japanese Patent Laid-Open Publication No. H5-311424, Japanese Patent Laid-Open Publication No. H1-248538). Further, also proposed is a pure copper target or a target in which 0.04 to 0.15 wt % of Ti is added thereto (for example, c.f. Patent Document 3).
And, in the foregoing proposals, rapid cooling for the uniform dispersion of the added elements, or continuous casting for preventing the segregation of added elements in ingots, cracks during casting, and coarsening of ingots are being proposed.
Nevertheless, although high purity copper or copper alloy which add minute amounts of metal to the high purity copper have an advantage in that the specific resistance is low, these cannot necessarily be considered favorable materials since there is the problem of electromigration and the problem of oxidation resistance during the process.
In particular, since the aspect ratio is becoming even higher in recent years (aspect ratio of 4 or higher), sufficient electromigration resistance and oxidation resistance are being sought.
In light of the above, as a wiring material, a proposal has been made for adding Al or Sn (or other various elements such as Ti or Zr) to copper to obtain a copper alloy to be used as the target (for example, c.f. Japanese Patent Laid-Open Publication No. H10-60633). Nevertheless, this is for improving the EM resistance, SM resistance or oxidation resistance without hindering the low resistance characteristics of copper, and could not be used for forming a seed layer in an ultra fine copper wiring process pursuant to the copper electroplating described above (for example, c.f. Japanese Patent Laid-Open Publication No. H6-177117.
Further, there is also a proposal stating that 0.5 wt % of Sn is effective in reducing the grain boundary diffusion and improving the EM characteristics of Cu (for example, c.f. [Electromigration and diffusion in pure Cu and Cu(Sn) alloy, Mat. Res. Soc. Symp. Proc. Vol. 427, 1996], Materials Research Society, written by C. H. Hu, K. L. Lee, D. Gup Ta, and P. Blauner (IBM)). Nevertheless, this does not resolve the coagulation problem (interaction) with the seed layer on the barrier layer formed with the likes of Ta or TaN.
Accordingly, with conventional technology, a wiring material for a semiconductor element, in particular, a copper alloy which allows the formation of a seed layer being stable, uniform and free from the occurrence of coagulation during copper electroplating has not been obtained, and conventionally technology was not necessarily sufficient.